/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.coders;



import com.bff.gaia.unified.sdk.values.TypeDescriptor;

import org.joda.time.Instant;



import java.io.*;



/**

 * A {@link Coder} for joda {@link Instant} that encodes it as a big endian {@link Long} shifted

 * such that lexicographic ordering of the bytes corresponds to chronological order.

 */

public class InstantCoder extends AtomicCoder<Instant> {

  public static InstantCoder of() {

    return INSTANCE;

  }



  /////////////////////////////////////////////////////////////////////////////



  private static final InstantCoder INSTANCE = new InstantCoder();

  private static final TypeDescriptor<Instant> TYPE_DESCRIPTOR = new TypeDescriptor<Instant>() {};



  private InstantCoder() {}



  @Override

  public void encode(Instant value, OutputStream outStream) throws CoderException, IOException {

    if (value == null) {

      throw new CoderException("cannot encode a null Instant");

    }



    // Converts {@link Instant} to a {@code long} representing its millis-since-epoch,

    // but shifted so that the byte representation of negative values are lexicographically

    // ordered before the byte representation of positive values.

    //

    // This deliberately utilizes the well-defined underflow for {@code long} values.

    // See http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.18.2

    long shiftedMillis = value.getMillis() - Long.MIN_VALUE;

    new DataOutputStream(outStream).writeLong(shiftedMillis);

  }



  @Override

  public Instant decode(InputStream inStream) throws CoderException, IOException {

    long shiftedMillis;

    try {

      shiftedMillis = new DataInputStream(inStream).readLong();

    } catch (EOFException | UTFDataFormatException exn) {

      // These exceptions correspond to decoding problems, so change

      // what kind of exception they're branded as.

      throw new CoderException(exn);

    }



    // Produces an {@link Instant} from a {@code long} representing its millis-since-epoch,

    // but shifted so that the byte representation of negative values are lexicographically

    // ordered before the byte representation of positive values.

    //

    // This deliberately utilizes the well-defined overflow for {@code long} values.

    // See http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.18.2

    return new Instant(shiftedMillis + Long.MIN_VALUE);

  }



  @Override

  public void verifyDeterministic() {}



  /**

   * {@inheritDoc}

   *

   * @return {@code true}. This coder is injective.

   */

  @Override

  public boolean consistentWithEquals() {

    return true;

  }



  /**

   * {@inheritDoc}

   *

   * @return {@code true}. The byte size for a big endian long is a constant.

   */

  @Override

  public boolean isRegisterByteSizeObserverCheap(Instant value) {

    return true;

  }



  @Override

  protected long getEncodedElementByteSize(Instant value) throws Exception {

    if (value == null) {

      throw new CoderException("cannot encode a null Instant");

    }

    return 8;

  }



  @Override

  public TypeDescriptor<Instant> getEncodedTypeDescriptor() {

    return TYPE_DESCRIPTOR;

  }

}